The invention relates to a process for the production of a free flowing, powdered elastomer, filled with silicic acid, by precipitating an elastomer latex in the presence of silicic acid and an auxiliary precipitant with the aid of acids, as well as to a powdered elastomer obtained in accordance with this process.
The production of free flowing, silicic-acid-filled, powdered elastomer grades has been known for some time. Numerous publications deal wtih different versions of the method. An essential feature of all procedures is coprecipitation of silicic acid (starting with water glass) and elastomer (from latex). An over-all drawback of these processes resides in the formation of large quantities of liquid which normally contain high proportions of electrolytes. Grave wastewater treatment problems are the result.
Such a process is disclosed, for example, in German Patent No. 2,030,172. In addition to the general, above-mentioned drawbacks of the process, the product is not a free flowing, powdered elastomer that can be further processed immediately. Even if a free flowing powder is obtained, the powder grain is too large. Therefore, additional grinding operations must be performed in any event. On the other hand, the patent expressly demonstrates by experiments that the desired results are not achieved by separate precipitation of silicic acid, i.e., elimination of coprecipitation, and subsequent mixing of precipitated silicic acid with the elastomer.
Also, a process has been known for precipitating elastomer latices in the presence of silicic acid (German Patent No. 1,224,481). However, this process does not involve the production of free flowing powdered elastomer. Rubber crumbs are obtained, which were the usual product at the time the application for this patent was filed. The silicic acid disclosed therein is not defined in any greater detail. Merely the examples mention the size of the surface area of the primary particles. Nothing is said about the surface area and structure of the secondary particles.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.